1. Field of the Invention
The present invention relates to a pipeline valve apparatus and, more particularly, to improvements in sealing and flow characteristics of valves.
2. Description of the Invention Background
Heretofore, valve bodies have been constructed in various forms, two of which include spherical bore valve bodies which were adapted to receive ball valves and cylindrical bore valve bodies which were adapted to receive butterfly valves. There are several disadvantages associated with these valve forms. The spherical bore valve body with a ball valve, although providing satisfactory sealing characteristics provides poor throttling characteristics. While such valves may be adequate when only fully open and fully closed valve positions are required, when throttling is required, cylindrical bore valve bodies with butterfly valves are preferred.
However there are problems associated with cylindrical bore valve bodies, one of which is that the butterfly valve must have a smaller diameter than the bore of the body. In the event of catastrophic failure of the shaft which rotates the valve, the valve may travel downstream, posing a risk to workers and equipment. Another problem with prior butterfly valves is that they are rotated by means of a shaft which is inserted into the disk. Such valves require hubs built into the disk to receive the shaft. Thus, it is necessary to provide a disk with a hub area having a greater diameter than the shaft. The enlarged hub areas, especially in the smaller valves, such as valves in the 4 inch and smaller pipeline range, produce a significant flow restriction through the pipe even when disk is rotated to the full open position. Additionally, due to the cylindrical bore in the valve body, flow is limited through the valve body because of the minimal relative distance between the disk and the inside surface of the valve body. Such severe flow restrictions associated with butterfly valves having cylindrical bore valve bodies render such valves undesirable in many applications.
Therefore, control valves especially in the 4 inch and smaller pipeline range need the desirable characteristics of both butterfly valves and ball valves but which eliminate the undesirable characteristics of such valves. A valve is needed which has increased flow through the valve body when fully open and which has excellent throttling characteristics. A valve is also needed which will not travel downstream should catastrophic shaft failure occur.
The demand for control valves to perform in very hostile chemical environments has caused valve manufacturers to produce a variety of very different butterfly and ball valve product lines within each company. Unfortunately, each product line requires its own engineered and manufactured components, a situation producing significant cost increase at both the manufacturing and customer levels.
Manufacturability poses another problem in many valve designs, and the ball and butterfly valves are no exception. The disk's concentricity to the valve housing seat requires very rigid design standards and expensive machine tooling. A valve body or disk machined out of tolerance produces higher cost in scraped components, and/or valves in service with components at borderline tolerances will inevitably generate higher maintenance costs.
Another problem with valves used in the past is that it is difficult to obtain an effective seal between the valve body and the control shaft. Valves in the past utilized stuffing boxes with packing rings which had to be forced against the smooth surface of the control shaft to effectuate a proper seal. Relatively high forces were required to maintain such a seal between the packing rings and the smooth surface of the control shaft.
Additionally, it is desirable to provide a valve which eliminates fugitive emissions of any chemical identified as hazardous. Therefore, a valve design is needed that will minimize the present shaft high friction forces, while allowing safe and reliable performance within acceptable fugitive emissions limits.
The present invention is directed toward an improved design for a valve apparatus which overcomes, among others, the above discussed problems.